1. Field of the Invention
The present invention relates to telecommunications, and more particularly to a method and system for providing remote telephone service via a wireless local area network link.
2. Description of Related Art
In recent years, wireless local area networking has become increasingly popular. Provided with a suitable wireless communication device, a user operating in a wireless local area network (WLAN) can conveniently gain access to network resources without being tethered to a fixed location.
A WLAN can take various forms, one of the most common of which is that described by industry standard IEEE 802.11 (as modified by 802.11b and 802.11a). Applicable details of 802.11 are well known to those of ordinary skill in the art. Other examples of WLAN technology include Bluetooth and HomeRF. And still other examples are now known or will be developed in the future.
Generally speaking, in an 802.11 WLAN (by way of example), one or more access points (APs) are provided as base stations to interface between wireless terminals and a distribution system (e.g., a wired Ethernet or other system). When a wireless terminal first enters an 802.11 WLAN, the wireless terminal becomes associated with a nearby AP and becomes authenticated for purposes of communicating within the WLAN. Depending on the scope of authentication, the wireless terminal may then be able to communicate with other wireless terminals operating on the WLAN and/or with various servers or other entities in the distribution system. Further, the distribution system may provide connectivity with another network such as the Internet for instance. Therefore, the wireless terminal might be able to access resources on that other network as well.
In a typical arrangement, when a private (or pseudo-private) distribution system provides connectivity with a public network such as the Internet, the private system may include a firewall, such as a network address translator (NAT), to secure entities on the private system from exposure to the public network. (NAT is described in Network Working Group Request For Comments (RFC) 1631, “The IP Network Address Translator (NAT),” dated May 1994.) For instance, a NAT router at the edge of the private system could translate between private IP addresses in the private system and public (registered) IP addresses in the public network.
That is, each entity in the private system can have a private (unregistered) IP address to facilitate routing within the private system, and a router or other device sitting at the edge of the private system can have one or more public IP addresses. When an entity in the private system sends a packet to a public IP address, the router would translate the private source address in the packet's header into a particular public IP address/port before routing the packet to its destination in the public network. And when the router then receives an incoming packet destined for that particular public IP address/port, the router would then translate the destination IP address in the packet's header into the private IP address of the entity before routing the packet to the entity in the private network.
While NAT firewalls can work well to secure a private network, however, they can pose problems when it comes to communicating real-time media, such as voice. The reason for this is that most real-time media communications involve both signaling packets (e.g., H.323, RTCP or SIP signals) and bearer packets, and the signaling packets typically follow a protocol that contains address information not just in packet headers but also deeper within the packets, such as within the application layer (usually the payload portion of the packets). Conventional application of NAT to outgoing signaling packets would thus make the packets seem outwardly (in their headers) as if they came from a public network address, but the signaling messages within the packets would reflect the private network address. Consequently, resulting communications (signaling or bearer) from a remote entity in the public network would likely end up being directed to the private address and therefore not make it back to the private network.